Emulsifiers for amino resins

ABSTRACT

A mixture comprises an amino resin and a polymer which consists to the extent of at least 80% by weight of C 2 - to C 3  alkylene oxide groups.

[0001] The invention relates to a mixture comprising an amino resin anda polymer which consists to the extent of at least 80% by weight of C₂-to C₃-alkylene oxide groups.

[0002] The invention also relates to amino resins comprising covalentlybonded polymers as defined above. The invention relates in particular toaqueous dispersions of these mixtures with amino resins and to the useof the mixtures, amino resins, and/or their aqueous dispersions ascuring agents in coating compositions.

[0003] Because of their reactivity, especially to hydroxyl, amino resinsare used as curing agents for polymeric binders. In paint chemistry,hydrophobic, water-insoluble amino resins have been found particularlyadvantageous. In the case of aqueous coating compositions, the use ofwater-insoluble amino resins is of course more difficult. EP 733 686discloses dispersing the amino resins with an anionic emulsifier.

[0004] The curing agent is added to the coating composition only by thepaint manufacturer. In this case it is particularly important to thepaint manufacturer that this curing agent can be used both in aqueouscoating compositions and in coating compositions which are dissolved inorganic solvents. In this context, irrespective of the chosen coatingcomposition, a long shelf life, ready processability and goodperformance properties of the coatings subsequently obtained should beensured. In the case of the aqueous amino resin dispersions of EP 733686, their use in coating compositions based on organic solvents leadsto disadvantageous properties, for example deficient water resistance ofthe resulting coatings.

[0005] U.S. Pat. No. 3,310,416 discloses water-insoluble amino resinscomprising polyethylene glycols. These amino resins are used asdispersants, for example for hydrocarbons or polysiloxanes.

[0006] It is an object of the present invention to provide amino resinswhich are suitable as curing agents for aqueous coating compositions andfor coating compositions based on organic solvents.

[0007] We have found that this object is achieved by the initiallydefined mixtures, amino resins and their aqueous dispersions.

[0008] The amino resin which is a constituent of the mixture comprisesreaction products of aldehydes, for example glyoxal, furfurol and,preferably, formaldehyde, with amino compounds, such as urea oraminotriazine, for example benzoguanamine, acetoguanamine and,preferably, melamine.

[0009] Preference is given to amino resins based on aminotriazines.Reaction products of melamine and formaldehyde are particularlypreferred.

[0010] In the course of the reaction of aldehyde, especiallyformaldehyde, the amino groups of the aminotriazines have beenalkylolated, especially methylolated; in other words, the hydrogens ofthe amino groups are replaced by alkylol groups. Preferably more than30%, in particular more than 50% of the hydrogens are replaced byalkylol groups. As a result, for example, of condensation reactions ofthe alkylol groups, the amino resins may contain a plurality ofaminotriazine rings. Preferably they contain on average from 1 to 20aminotriazine rings.

[0011] The remaining alkylol groups are preferably etherified,extensively or fully, with alcohols, preferably with C₁- toC₁₆-alkanols. These are preferably butanol or mixtures of butanol andmethanol predominantly containing butanol.

[0012] The amino resins are preferably insoluble in water.

[0013] The dilution number of the amino resins is preferably less than20 and, with particular preference, less than 5, in particular less than2 or 1 g. The dilution number is a measure of how much hydrophilicsolvent can be mixed with an amino resin without the resulting solutionbecoming cloudy.

[0014] The dilution number is determined by the following method:

[0015] 1 g of amino resin is placed in a 25 ml test tube. Then 0.5 gportions of water are added at 23° C. After each portion has been addedthe tube is shaken and observed to see whether clouding or phaseseparation (incompatibility) remains after shaking. The amount of water,in g, added when incompatibility occurs is the dilution number.

[0016] For this purpose the polymer can be added, for example, to theamino resin solution as obtained in the preparation of the amino resin,in an organic solvent, generally the etherifying alcohol.

[0017] The resulting mixture can then be converted into an aqueousdispersion of the amino resin by adding water.

[0018] The polymer can also, for example, first be dissolved in waterand the aqueous solution added to the amino resin.

[0019] The resulting aqueous dispersion of the amino resin can then beused as a curing agent in aqueous coating compositions.

[0020] In principle it is of course also possible to add the amino resinand the polymer, separately or together, directly to the aqueous coatingcomposition and then to disperse the amino resin therein with the aid ofthe polymer.

[0021] Another embodiment of the invention comprises reacting thepolymer with the water-insoluble amino resin; in other words, some ofthe alkylol groups of the amino resin are etherified with this polymer.This case is also subject to the above statements regarding the aminoresin, the polymer and the proportions by weight of the two; in formulaeI and II, one of the radicals R¹ and R² is replaced by the bond to theamino resin. The amino resin obtained by reaction with the polymer isstill insoluble in water and has the above dilution number, but can bedispersed in water, as described above for the mixture, and is usedaccordingly as a curing agent in coating compositions.

[0022] Coating compositions comprise a polymeric binder with or withoutfurther additives such as pigments, dyes, leveling agents, thickeners,etc.

[0023] The polymeric binder, owing to its content of active hydrogens(OH, NH, SH groups), can be crosslinked with amino resins, i.e. iscurable.

[0024] Examples of suitable binders are alkyd, polyester, epoxy andpolyurethane resins, free-radical polymers based on acrylates, vinylesters, dienes and vinylaromatic compounds or mixtures thereof.

[0025] In addition to the amino resin, the novel mixture comprises apolymer which consists to the extent of at least 80% by weight,preferably to the extent of at least 90% by weight, of C₂- toC₃-alkylene oxide groups. These groups can be exclusively ethylene oxidegroups, propylene oxide groups, or ethylene oxide and propylene oxidegroups.

[0026] The polymer preferably contains on average at least 10 and, withparticular preference, at least 20 alkylene oxide groups. The maximumnumber of these groups is preferably 500, particularly preferably 300and, with very particular preference, 200.

[0027] Preferred polymers are those of the formulae

[0028] where R¹ and R² independently are hydrogen, C₁- to C₂₀-alkyl orC₁- to C₂₀-acyl.

[0029] Preferably, R¹ and R² are hydrogen or C₁-C₄-alkyl, especiallymethyl or n-butyl.

[0030] The variables x, y, z are preferably at least 1. Preferablytherefore, both formula I and formula II represent 3-block copolymers(EO-PO-EO in formula I and PO-EO-PO in formula II).

[0031] Polymers of this kind are known and are obtainable commerciallyfrom BASF, for example, under the designation Pluronic®.

[0032] The content of the polymer in the mixture is preferably from 0.1to 50 parts by weight, particularly preferably from 0.5 to 10 parts byweight, based on 100 parts by weight of amino resin.

[0033] The polymer serves as an emulsifier, in other words a dispersant,for dispersing the water-insoluble amino resin in water.

[0034] Preference is given to free-radical addition polymers,condensation polymers or polyaddition polymers having OH groups,preferably with a hydroxyl number of from 20 to 200 mg of KOH/g of solidmatter (in accordance with DIN 53240).

[0035] The binder and therefore the coating compositions as well can bepresent, for example, in the form of solutions in water or organicsolvents or in the form of aqueous dispersions.

[0036] A significant advantage of the invention is that the novelmixtures and the novel amino resins modified with the polymers, or theaqueous dispersions of these mixtures and amino resins, can be used ascuring agents both for aqueous coating compositions and for coatingcompositions in organic solvents, and in both cases give coatings havinggood performance properties, in particular good water resistance andadhesion.

[0037] The aqueous dispersions of the mixtures or of thepolymer-modified amino resins are stable on storage. The coatingcompositions which comprise the mixtures or the polymer-modified aminoresins are also stable on storage.

[0038] The novel coating compositions which comprise a polymeric binderand the novel curing agent can be applied to any desired substrates, forexample of wood, metal, paper or plastic, by any desired methods, forexample spreading, knife coating or spraying.

[0039] Following application, curing and removal of water and/or organicsolvent take place in general by drying at elevated temperatures or bystoving.

EXAMPLES

[0040] A Polymers (emulsifiers)

[0041] A1 Pluronic® PE 6400 (PO-EO block copolymer, molar mass of thepoly-PO-block 1750, EO content 40% by weight).

[0042] A2 Pluronic® PE 6800 (PO-EO block copolymer, molar mass of thepoly-PO-blocks 1750, EO content 80% by weight).

[0043] A3 Pluronic® PE 9400 (PO-EO block copolymer, molar mass of thepoly-PO-blocks 2750, EO content 40% by weight).

[0044] A4 (Comparison) Emulphor® OPS 25 (ethoxylated sodiump-octylphenol sulfate, 25 mol of EO per mole of alkylphenol); 34%strength by weight solution in water

[0045] B) Amino resins

[0046] B1 Luwipal® LR 8891 (butylated, partially alkylatedmelamine-formaldehyde resin in n-butanol, solids content 75%).

[0047] B2 Luwipal® LR 8817 (methylated, partially alkylatedbenzoguanamine-formaldehyde resin in isobutanol, solids content 80%).

[0048] B3 80 ml of butanol are distilled off at 50 mbar from 1000 g ofLuwipal® LR 8891 with a solids content of 75%. The concentrate is thenadjusted to a solids content of 72% with 115 ml of butylglycol.

[0049] B4 80 ml of butanol are distilled off at 50 mbar from 1000 g ofLuwipal® LR 8891 with a solids content of 75%. 24 g of A3 (=2.3% byweight, based on A3 and B1) are then added and the concentrate isadjusted to an amino resin content of 72% with 115 ml of butylglycol.

[0050] B5 985 g of Luwipal® LR 8891 with a solids content of 75% byweight are admixed with 2.8 g of p-toluenesulfonic acid monohydrate and7 g of A2. 190 ml of butanol are distilled off under reduced pressure atinternal temperatures of 85° C. -95° C. Then the p-toluenesulfonic acidis neutralized with 105 mol-% of dimethylethanolamine, and 120 ml ofbutylglycol are added at 60° C. The result is an A2-modified amino resinhaving a solids content of 75%.

[0051] B6 2.3% by weight of A4 (solids) are dissolved in amino resin B1(weight based on the sum of A4, solids, and B1)

Use Examples

[0052] C) Preparing aqueous melamine resin emulsions

[0053] Method I: Adding the emulsifier to the amino resin

[0054] 60 g of the amino resin solution, containing the emulsifier, arecharged to a 150 ml polyethylene beaker, and the amount of watercalculated to lead to an amino resin emulsion having a solids content of45% is added dropwise over the course of 10 minutes while all the timestirring at from 500 to 1000 rpm with a laboratory stirrer fitted withdissolver disk. Stirring is subsequently continued for 30 minutes.

[0055] Method II: Adding the emulsifier to water

[0056] 60 g of the amino resin solution are charged to a 150 mlpolyethylene beaker, and the aqueous solution, containing theemulsifier, which is calculated to lead to an amino resin emulsionhaving a solids content of 45% is added dropwise over the course of 10minutes while all the time stirring at from 500 to 1000 rpm with alaboratory stirrer fitted with dissolver disk. Stirring is subsequentlycontinued for 30 minutes.

[0057] The following characteristics are measured for the fine emulsionswhich result (pH values with a glass electrode at 23° C., viscositieswith a Brookfield viscometer, spindle 3, 10 rpm, 23° C.): Amount ofemul- sifier Visco- Amino (% by pH sity Example Method resin Emulsifierwt.) value (Pas) C1  I B4 A3 2.3 4.8 2.8 C2  I B5 A2 0.7 5.5 1.25 C3  IB6 A4 2.3 6.1 0.35 (Compari- (Compari- son) son) C4 II B1 A1 1.4 5.6 1.9C5 II B2 A2 0.7 8.0 0.45 C6 II B3 A3 0.7 5.6 2.0 C7 II B1 A4 0.7 6.6 0.9(Compari- (Compari- son) son)

[0058] D) Aqueous polyester stoving enamel

[0059] Example D1:

[0060] 38 g of a 55% strength polyester resin solution (Bayhydrol® D155)in 16.5% butylglycol, 6.8% isobutanol, 18% water and 3.7%dimethylethanolamine, having a hydroxyl content (solvent-free) of 1.5%and an acid number (solvent-free) of 42 mg of KOH/g, are diluted with 42g of water, and then 20 g of the melamine resin emulsion C1 are addedwith stirring. This gives a 30% strength aqueous polyester varnishhaving a viscosity at 23° C. of 3.2 Pas.

[0061] Comparison Example D2:

[0062] The procedure of D1 is repeated but using, instead of themelamine resin emulsion C1, the comparison emulsion C3: varnishviscosity at 23° C.: 2.0 Pas.

[0063] Comparison Example D3:

[0064] The procedure of D1 is repeated but using, instead of themelamine resin emulsion of Example C1, 11 g of an 80% strength aqueoussolution of methanol-etherified, partially alkylated Luwipal® 073. Thisis therefore a water-soluble melamine resin without added emulsifier.Dilution with 25 g of water gives a 40% strength polyester varnish.Varnish viscosity at 23° C.: 4.2 Pas.

[0065] Condensation water testing:

[0066] The aqueous varnishes D1-D3 are applied with a 200 μmfilm-drawing frame to 200×90×0.75 mm deep-drawn metal panels, vented atroom temperature for 10 minutes, dried first at 50° C. for 10 minutesand then stoved at 130° C. in a convection oven for 20 minutes. Thisgives transparent coatings having a film thickness of from 20 to 25 μm.After waiting for 24 hours, the test panels are stored with the coatedside downward for 7 days over a water bath at 60° C. After a further 7days of storage at 50% relative atmospheric humidity and 23° C, thefollowing differences are observed.

[0067] The coating with the novel aqueous varnish D1 is unchanged, thecomparison coating with the aqueous varnish D2 containing an ionicemulsifier has experienced subfilm corrosion over its entire area, andthe comparison coating with the aqueous varnish D3 containing amethanol-etherified melamine resin shows cracking and delamination overthe entire area, and furthermore the test panel has corroded.

[0068] E) Solvent borne acrylate clearcoat

[0069] General preparation procedure:

[0070] 50 g of an OH-containing polyacrylate (Luprenal® 240 S) having anOH number of 65 mg of KOH/g and a solids content of 60% by weight, and20 g of amino resin (solids), and an amount of hydrocarbon (Solvesso®100) sufficient to give a solids content of 50% by weight, are used toprepare, by stirring, a clearcoat. Acrylate clearcoat Amino resinViscosity at 23° C. E1 (Comparison) B1 150 mPas E2 B4 155 mPas E3(Comparison) B6 155 mPas

[0071] Testing in a gradient oven

[0072] The solventborne clearcoat is applied with a 200 μm film-drawingframe to a 567×90×0.75 mm deep-drawn metal panel, vented for 10 minutesand stoved in a gradient oven, model 2612, from Byk, for 30 minutes overa temperature range from 90° C. to 190° C. After storage for 24 hours at50% relative atmospheric humidity and 230° C., the following tests arecarried out in succession in the individual temperature zones:

[0073] The flow is determined visually.

[0074] The water resistance of one side of the coated panel is tested bystoring it for 60 minutes, standing on the long edge, in a water bath,submersed to a depth of about 3 cm, and then the minimum stovingtemperature is determined which is necessary to obtain a nonabradable,finger-nail hard, optically unchanged coating.

[0075] The film thickness is determined using a Deltascopefilm-thickness meter from Fischer, Sindelfingen.

[0076] The pendulum attenuation is determined in accordance with DIN53157 using a model 5840 instrument from Byk.

[0077] The crosshatch test is carried out in accordance with DIN 53151using a crosshatching knife and Tesa film adhesive tape.

[0078] The Erichsen indentation is determined in accordance with DIN53156 using a model 5313 instrument from Byk.

[0079] Results: E1 E2 E3 (Amino resin (Amino resin (Amino resin B1) B4)B6) Flow good good good Water resistance 160 160 >190 from ° C.Temperature zone 120 150 180 120 150 180 120 150 180 (° C.) Filmthickness 40 40 40 39 39 38 40 39 38 (μm) Pendulum attenuation 89 92 9670 90 93 63 86 91 (deflections) Crosshatch 4.5 5 4 4 4.5 3.5 4.5 5 3(rating 0-5) Erichsen 7.7 4.7 2.7 7.6 4.8 2.5 6.1 3.8 2.2 indentation(mm)

[0080] Discussion of the results:

[0081] The amino resin B4, which contains the novel emulsifier, does notcause any impairment of the properties in solventborne coatingmaterials. The amino resin B6, which contains an emulsifier according toEP 733 686, leads to a deterioration in the water resistance.

1. An aqueous dispersion of a mixture comprising a water-insoluble aminoresin and a polymer which consists to the extent of at least 80% byweight of C₂- to C₃-alkylene oxide groups.
 2. An aqueous dispersion asclaimed in claim 1, where the content of the polymer is from 0.1 to 50parts by weight based on 100 parts by weight of amino resin.
 3. Anaqueous dispersion as claimed in claim 1 or 2 where the polymer containsat least 10 alkylene oxide units.
 4. An aqueous dispersion as claimed inany of claims 1 to 3 where the polymer is of the formula

where R¹ and R² independently are hydrogen, C₁- to C₂₀-alkyl or C₁- toC₂₀-acyl and x, y, z are an integer from 0 to 100 with the proviso thatthe sum of x+y+z is at least 10 or is a block copolymer of the formula

where R¹ and R² are as defined above and u, V, w are an integer from 1to 100 with the proviso that the sum of u+v+w is at least
 10. 5. Anaqueous dispersion of a water-insoluble amino resin comprisingcovalently bonded polymers which are the polymers as defined in any ofclaims 1 to
 4. 6. The use of an aqueous dispersion as claimed in any ofclaims 1 to 5 as a curing agent in a coating composition.
 7. The use asclaimed in claim 6, wherein the coating composition is an alkyd resin, apolyester resin, a polyurethane resin, a free-radical polymer based onacrylates, vinyl esters, dienes and vinylaromatics or a mixture thereof.